Application of semiconductors to ignition circuitry



y 1961 J. L. WILLIAMS ETAL 2,985,797

APPLICATION OF SEMICONDUCTORS TO IGNITION CIRCUITRY Filed 001;. 50-, 1958 INVENTOR3 James L. Williams 8 John G. Roberts BY FCI p ATTORNEY WITNESSES A Kai/4% United States Patent APPLICATION OF SEMICONDUCTORS TO IGNITION CIRC'UITRY James L. Williams, Prairie Village, Kans., and John G. Roberts, Cincinnati, Ohio, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation' of Pennsylvania Filed Oct. 30, 1958, Ser. No. 780,914 3 Claims. (Cl. 315-209) This invention relates to aircraft engine ignition systems and more particularly to an improvement in the existing low voltage, high energy capacitor discharge ignition systems.

One broad object of this invention is to eliminate all moving parts from the existing ignition systems and thus effect a greater reliability.

Another object of this invent-ion is the provision of arc ignition system that is smaller in size and thus less in weight and cost than the existing prior art ignition systems.

Other objects of this invention comprise an ignition system having lower power requirements, less radio interference, higher efilciency, and faster operation than the existing prior art ignition system.

Other objects and advantages will become more apparent from a study of the following specification and the accompanying drawing.

The accompanying drawing shows the invention in diagrammatic form as applied to a portion of the circuitry now in vogue with aircraft jet engine ignition systems.

A better understanding of the contribution to the prior art can very likely be had from a study of a portion of the existing prior art circuitry.

Let the assumption be that the transformer T has its primary winding TP supplied with an alternating current input. The transformer steps the voltage up to some higher value. This higher output voltage from the secondary TS is rectified by the rectifiers RBI, RE2, RE3, etc. The purpose of the rectifiers in series is to provide a rectification of a relatively high voltage. The number of rectifier tubes in series will depend on the output voltage, and the number needed will be directly proportional to the output voltage.

The rectified voltage from the rectifier tubes charges the capacitor C2 and the charge will rise until the breakdown voltage of the spark gap tube SGT is reached. This spark gap tube is a gaseous tube which will conduct large transient current at the instant the spark gap tube breaks down. This breakdown of the spark gap tube usually occurs at from 1 to kilovolts.

Upon conduction of the spark gap tube, the high volt age stored in the charged capacitor C2 is discharged through the spark igniter, or igniter plug IP. The igniter plug IP is a shunted surface gap type spark plug, having the high resistance shunt R2, which will fire at a very low voltage. This firing voltage is between 800 and 1800 volts and is very low with reference to voltage at the capacitor terminals of capacitor C2 when this capacitor begins to discharge.

In view of the low firing voltage of the spark plug this ignition system is usually called a low voltage, high en ergy capacitor discharge ignition system. This system has an advantage over other systems due to the large availability of electrical energy at a comparatively low voltage. In this case,

Electric energy= CE.

where C=the capacitance of the capacitor C2 and E: the charging voltage of the capacitor C2.

Another advantage of this system lies in the use of the shunted surface igniter plug IP. This advantage is due 0 the physical properties of the shunted surface plug which allows it to fire at a rather low voltage (800 to' 1800 volts) and to the physical construction which does not allow the plug to foul even when the firing end is covered with raw fuel or even carbon.

In the existing prior art circuitry the alternating current input to the transformer T is obtained from an involved alternating current supply or from a direct current supply by the use of elaborate, heavy and expensive switching means.

The broad novel features of this ignition system is the substitution of a simple oscillator circuit which allows the use of a direct current power input without having to use a mechanical vibrator, or other rapidly operating switching means, to provide the electrical pulses which are necessary to provide proper transformer action.

In this mentioned simple oscillator, B represents the direct current supply and S a switch for connecting the resistor R1 and inductance coil' L and capacitor C1 to the source of direct current. A hyperconductive negative resistance diode, known as a Dynister, is connectedin series with the primary winding TP and these elements are connected across the terminals of the capacitor C1.

The operation of this oscillator circuit is as follows. The instant switch S is closed, the capacitor C1 begins to charge, the charging rate is rather high, and is merely limited by the resistor R1 and inductance coil L.

At, or near, full charge of the capacitor C1 the voltage at the terminals of the Dynister Dy becomes sufficiently high for the diode to break down and become conducting and thus a surge of current flows through the primary winding TP. The resistor R1 and inductance L allows the capacitor C1 to discharge and repeat the cycle again and again as long as switch S remains closed. The necessary pulsating current is thus supplied to the transformer, thus providing the proper transformer action necessary to operate the ignition unit. Proper selection of the resistor R1, inductance coil L, and capacitor C1, can provide a very rapid charging rate for the capacitor C1, and an operation of the transformer primary TP at a higher voltage than the voltage of the direct current input B.

From the foregoing it will be apparent that all mechanical oscillators and switching means are eliminated. Further mechanical oscillators are limited to frequencies equal to and less than cps. The circuit herein disclosed may be tuned to one kc. and thus give a much higher spark rate than prior art devices.

The circuit herein disclosed can be used to great advantage in the jet engine and possibly in the rocket engine ignition field. In these and other fields the great advantage of the circuitry herein disclosed over existing prior art ignition systems lies in the large reduction in size and weight and the removal of all mechanical moving parts.

While but one embodiment has been disclosed the invention is not limited to the one showing but includes such modifications as fall within the spirit and scope of this invention.

We claim as our invention:

1. In a low voltage, high energy capacitor discharge ignition system, including a shunted surface gap type spark plug, a spark gap tube connected in series with the plug, a charging capacitor connected across the tube and plug, current rectifying means, a transformer having a low voltage primary winding and a high voltage output secondary winding, said secondary winding being connected in a loop circuit with the rectifying means and the capacitor, in combination with, a source of direct current, switching means, an electric oscillator circuit tuned to a relatively high frequency connected through said switching means to the primary winding and to the source of direct current, said oscillator circuit including a capacitor and impedance means connected in a loop circuit with the source of direct current by said switching means, and a hyperconductive negative resistance diode connected in series with the primary winding and selected to break down and conduct to discharge the capacitor each time the charge on the capacitor is increased to a selected magnitude.

2. In a low voltage, high energy capacitor discharge ignition system, including a shunted surface gap type spark plug, a spark gap tube connected in series with the plug, a charging capacitor connected across the tube and plug, current rectifying means, a transformer having a low voltage primary winding and a high voltage output secondary winding, said secondary winding being connected in a loop circuit with the rectifying means and the capacitor, in combination with, a source of direct current, switching means, an electric oscillator circuit including a hyperconductive negative resistance diode, connected in series with the primary winding, a capacitor connected across the primary winding and the diode connected in series with the primary winding, and impedance means connected through said switching means in a loop circuit with the last named capacitor and the source of direct current.

3. In a low voltage, high energy capacitor discharge ignition system, including a shunted surface gap type spark plug, a spark gap tube connected in series with the plug, a charging capacitor connected across the tube and plug, current rectifying means, a transformer having a low voltage primary winding and a high voltage output secondary winding, said secondary winding being connected in a loop circuit with the rectifying means and the capacitor, in combination with, a source of direct current, switching means, an electric oscillator circuit including a resistor, a capacitor, and an inductance connected through said switching means in a loop circuit with the source of direct current, a hyperconductive negative resistance diode connected in series with the primary winding, and the last named capacitor being connected across the series circuit formed by the primary winding and said hyperconductive negative resistance diode.

References Cited in the file of this patent UNITED STATES PATENTS 2,328,444 Francis Aug. 31, 1943 2,347,286 Sandretto Apr, 25, 1944 2,544,477 West Mar. 6, 1951 2,571,789 Tognola Oct. 16, 1951 2,837,698 Segall June 3, 1958 

